Self-lubricating bearings and other machine elements and a process for their manufacture

ABSTRACT

Self-lubricating bearings and other machine elements are prepared by admixing perfluoroalkylene polymers such as polytetrafluoroethylene with defined inorganic solid lubricants and epoxy resins followed by a cold molding technique and heating cycle which allows the economical production of large numbers of self-lubricating parts with excellent precision and low dimensional change.

Machine elements subject to mutual relative motion are usuallylubricated by a lubricant introduced between these parts. However,modern developments are aimed at using self-lubricating machineelements.

It is known that self-lubricating machine elements can be produced byusing so-called lubricant coatings containing solid lubricants such aszinc sulphide, calcium fluoride, polytetrafluoroethylene and, inparticular, molybdenum disulphide. Synthetic resins such as epoxy resinsand polyvinyl butyrals dissolved in solvents are used as the binder forthe solid lubricants. These preparations are applied to the articlesand, after drying or by the action of heat, yield thin dry lubricantfilms. The disadvantage is that such films possess relatively shortuseful lives.

It is further known that sliding machine elements can be entirelyproduced from low-friction materials. Thus machine elements have alreadybeen fabricated from polyamides with added molybdenum disulphide. Theaddition of molybdenum disulphide is aimed at improving the suitabilityof these plastics as a low-friction material. While such an additiondoes indeed increase the degree of crystallinity of the polyamide andhence leads to enhanced mechanical strength and reduced waterabsorption, the wear properties are not improved adequately, because theplastic does not withstand the loads at which the lubricating propertiesof the molybdenum disulphide become fully effective.

Further, self-lubricating bearings made of polytetrafluoroethylene areknown which are suitable for low loads and low sliding speeds. Thedisadvantage here is their inadequate hardness and cold flow under load,leading to bearing failure. It has, therefore, been proposed to improvethe properties of the polytetrafluoroethylene by using low frictionmaterials with polytetrafluoroethylene along with admixed graphite,molybdenum disulphide, glass fiber and metal powder; these can be usedunder somewhat higher loads and at higher sliding speeds but their wearoften is still too high.

It is known, further, to produce self-lubricating bearings fromcompositions consisting of polytetrafluoroethylene, molybdenumdisulphide and other solid lubricants, metal powder and liquid epoxyresin, by pouring into molds and subsequently curing. The disadvantageis that, because of their formulation, such compositions need to beprocessed by casting and therefore do not allow convenient noreconomical manufacture of a large number of elements. To achieve this,fabrication by cold molding would be required, but this is not possiblewith liquid compositions. In addition, casting does not lead to bearingsmeeting the required tolerances and the products need to be brought tothe required dimensions by an expensive finishing operation.

Other known bearing compositions with a self-lubricating action arecomposite substances of mosaic structure which are used in the form ofthin strips and which contain rigid lubricant particles with an averageparticle size greater than 0.075 mm. dispersed in a flexible matrixcomposition consisting preferably of organopolysiloxane elastomers,ethylene-propylene-diene terpolymers, elasticperfluoropropylene-vinylidene fluoride copolymers or2-chloro-1,3-butadiene polymers. The rigid particles having alubricating action consist of a rigid binder, for example, a cured epoxyresin in which solid lubricants are dispersed. These products arereadily usable in the form of thin strips. However, such compositebodies are not suitable for fabricating self-lubricating bearings in theform usually required in machine construction, and hence high toolingcosts hinder their economical mass production.

Because of the above noted disadvantages in cold molded bearings,sintered metal bearings are used very extensively today. These consistof porous metal bodies whose pores contain lubricating oil. Theirdisadvantage is that the amount of oil available for lubrication islimited. In addition, oil is thrown off when the shaft rotates at highspeed, oil leaks away from vertically positioned bearings and rapidaging of the oil occurs at elevated temperatures. Such bearings cannotbe employed under vacuum and at low temperatures, and under high loadsand at low sliding speeds since the load bearing capacity of the oil isinadequate and leads to metal-metal contact, a high degree of wear andeven seizing.

In contrast to known processes for producing self-lubricating machineelements, the cold molding process described herein offers theadvantages that it facilitates an economical production of large numbersof self-lubricating molded parts which show only minor wear at highstresses and, at high and low temperatures they have excellent hardnessand strength as well as low friction coefficients, they are maintenancefree during long periods of use and further, they are useful in systemswhere vacuum is required.

Thus, one object of this invention is a process for manufacturing moldedobjects made of self-lubricating lubricant material by mixing a powderyheat-curable eposy resin solid at 20° C. containing preferably curingagent and/or cross-linking catalysts with powdery inorganic solids,especially solid lubricants, homogenizing and pulverizing the mixtureinto a powder, mixing the powder with polytetrafluoroethylene, coldmolding into molded objects and curing the molded objects at increasedtemperatures, characterized by the fact that the epoxide resin and theinorganic solid material are mixed in ratio of 10 to 25 parts by weightof epoxide resin and 90 to 75 parts by weight of inorganic solids,plasticized and homogenizing the mixture at a processing temperatureabove the softening point of the epoxide resin, producing a powderymixture using pulverization and screening, this mixture having aparticle size in which more than 80 weight percent of the particles isless than 0.315 mm. in size, mixing the powder mixture with 2 to 30weight percent polytetrafluoroethylene, based on the total weight of allthree components and molding at room temperature at a molding pressureof 15-50 kp./mm.² which stands in a specific ratio to the amount ofpolytetrafluoroethylene used, and subsequently curing the molded objectsat increased temperatures up to 260° C. through a specific cycle.

In a surprising manner it has now been found that the deviation of themolded objects from the theoretical dimension can be decreased tomeasurements which are practically incapable of being measured, that theamount of one of the three components of the molding mixture, namelyperfluoroalkylene polymers and the applied molding pressure balance oneanother out. As will be explained in greater detail, within specificlimits for the amount of perfluoroalkylene polymers and moldingpressure, the desired tolerance accuracy will be achieved with adecreased addition of perfluoroalkylene polymer in combination with ahigher pressure or with a higher addition of perfluoroalkylene polymerin combination with a decreased molding pressure.

Cold molding masses from which the low tolerance, self-lubricatingformed articles are produced, according to the invention, consist ofthree components.

The first component is a powdered epoxide resin, heat curable and solidat room temperature which contains preferably a curing agent orcross-linking catalyst. The epoxy resin used for purposes according tothe invention must be a solid material under normal conditions sinceliquid epoxy resins are not suitable for processing using cold molding.Epichlorohydrin-bisphenol A condensates i.e., novolac resins (bisphenolA is 2,2-bis(4-hydroxyphenyl)-propane) with multi-epoxy functionality orcycloaliphatic epoxy resins which have epoxide equivalent weights in therange of 200 to 1000 are quite suitable. Curing agents and crosslinkingcatalysts can be for example, polycarboxylic acids, which are solids atroom temperature, and their anhydrides, as well as amines and amides inthe powdered form. The resins employed herein are well known and arefully described in Polymers and Resins by Golding, published by D. VanNostrand Co., Inc., 1959, Library of Congress catalogue Card No.59-8412.

The molding masses processed according to the process of the inventioncontain a second component, which is an inorganic solid material. Theinorganic solid materials used for purposes of the invention consist ofat least one and preferably two solid lubricants. In addition to solidlubricants the second component may also have reinforcing andnon-reinforcing filler material. Inorganic solid materials suitable forthe invention are metallic sulfides, especially MoS₂, WS₂ and ZnS,metallic oxides, for example ZnO, PbO and Ca(HO)₂, metal fluorides, forexample CaF₂, Na₃ AlF₆ and FeF₂, graphite, boron nitride, bariumsulfate, fiberglass, asbestos or other silicates with a fibrousstructure and carbon in the form of fibers. It is preferred not toemploy as inorganic solid materials, alkali metal sulphides, alkalineearth metal sulphides or alkali metal oxides as they do not give optimumproperties.

As a third component for this process, polyperfluoroalkylene polymersare used which have a molecular weight of 35,000 grams/mole to 100,000grams/mole.

Preferably, polytetrafluoroethylene (PTFE) wax is used but it is withinthe scope of this invention to use higher molecular weightperfluoroalkylene polymers having molecular weights of up to 150,000grams/mole and which, when used, have an average particle size of lessthan 0.075 mm.

The PTFE wax of this invention is a thermally degradable material with amolecular weight of 35,000 to 100,000 grams/mole, an average particlesize of 0.03 mm., a density of 2.25 to 2.27 and a melting point range of324 to 327° C. Such materials are commercially available.

It is also within the scope of this invention to utilizepolytetrafluoroethylene-perfluoropropylene copolymers having a molecularweight of less than 150,000 grams/mole.

It is a further object of this invention to utilize a composition formolding self-lubricating elements consisting essentially of

(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a solidthermosetting epoxy resin selected from a group consisting ofcondensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl) propane orepichlorohydrin and a cycloaliphatic epoxy resin;

(b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of inorganicsolid particles with an average particle size of less than 0.075 mm.selected from the group consisting of metal sulphides, metal oxides,metal fluorides, graphite, boron nitride, barium sulphate, glass fibers,asbestos, silicates with a fibrous structure or carbon in fibrous form,and

(c) 2-30 percent by weight of solid perfluoroalkylene polymers orcopolymers with a molecular weight of 35,000 to 150,000 grams/mole.

The process according to the invention is conducted in essentially five(5) major stages:

(1) The inorganic solid particles and the epoxy resin which contains acuring agent or crosslinking catalyst is made a homogeneous powderymixture by any known method.

(2) The mixture is plasticized and homogenized in an extruder,preferably in a planetary rolling extruder, or a double roll mill at aprocessing temperature above the softening temperature of the epoxyresin. When using a roll mill the one roll is correspondingly heated,the other may be cooled.

(3) The resulting material which may be in the form of coarse lumps orboards is reduced to a powder. Then by means of screening a sievefraction is produced with a particle size distribution consisting of atleast 80 weight percent particles with a particle size of less than0.315 mm.

The sieve fraction is intimately mixed with 2 to 30 weight percent ofpolyperfluoroalkylene based on the total weight of all three components.

(4) The molding mixture obtained in this way is molded with the knownsteel multi-cavity dies with a predetermined molding pressure based onthe added polytetrafluoroethylene, of 15 to 50 kp./mm.² at roomtemperature to form molded objects. Using the process according to theinvention up to 2000 self-lubricating, low tolerance molded objects,especially slide bearings can be produced per hour.

(5) The cold molded objects are cured finally in a heating oven atincreased temperatures up to 260° C. Preferably a heating cycle of 2hours is used at 170° C., 2 hours at 200° C. and 4 hours at 230° C.

It is essential in the invention that in order to achieve as littleshrinkage or swelling as possible, the required molding pressure andportion of molding mixture of polytetrafluoroethylene will have tobalance one another out and the inorganic solid material and epoxyresins which are used and their ratio will have to be balanced out aswill be evident from the following examples in which the invention isexplained in greater detail. The process is conducted as indicatedabove, in 6 hours. The molded objects produced are cured for 2 hours at170° C., 2 hours at 200° C., and finally for 4 hours at 230° C.

In accordance with the invention, cured molded products with excellentmechanical properties are obtained. In addition, bearing componentssuitable for use with heavy loads can be produced without metalbackings, becuase the exceptionally low friction values prevent theaccumulation of heat.

The invention will now be described in greater detail by way of thefollowing examples which are not to be considered as limiting the scopeof this application.

EXAMPLE 1

38 parts by weight molybdenum sulphide, 38 parts by weight zincsulphide, 15.9 parts by weight epichlorohydrin-bisphenol A epoxy resinand an epoxy equivalent weight of 475 to 575 and 3.1 parts by weight of1,2,3,4-cyclopentanetetracarboxylic acid dianhydride were admixed withone another, homogenized on the two-roll mill and ground to fine powder,5 parts by weight polytetrafluoroethylene with a loose bulk density of600 to 800 g./l., an average particle size of 0.030 mm., a specificgravity of 2.25 to 2.29, a melting range of 324 to 327° C. and amolecular weight of 35,000 to 100,000 grams/mole are then admixed. Thepowder mixture is processed further as described above. Measuredaccording to DIN 53,456, the ball indentation hardness of the curedmaterial is 22.9 kp./mm.².

EXAMPLE 2

To demonstrate the superiority of the molded bodies made fromself-lubricating low friction material, bearings produced by thisinvention using a molding composition consisting of 40 parts by weightof molybdenum disulphide, 40 parts by weight of zinc sulphide, 16.7parts by weight of the epoxy resin described in Example 1 and 3,3 partsby weight of 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride(designated "A" in the table below) is compared, with respect to thecoefficient of friction and the rate of wear, with bearings producedfrom the molding compositions described in Example 1. The coefficient offriction is determined with the A. A. Bartel lubrimeter at a PV of##EQU1## The rate of wear is determined on small electric motorssimulating practical conditions. The motor are allowed to run for 1000hours. After this period the change in the inner diameter due to wear ofthe bearing produced from the self-lubricating low friction material ismeasured and the rate of wear is calculated as the number of operatinghours producing wear of 0.001 mm. Two different motors are used for thetest. Motor 1 is operated at 1500 r.p.m., a speed of 0.63 m./sec. and aload of 0.28 kp./cm.², motor at 1500 r.p.m., a speed of 0.32 m./sec. anda load of 0.15 kp./cm.². The results are shown in the following table.

    ______________________________________                                                   Coeffi-                                                                              Rate of wear in                                                        cient of                                                                             hours                                                       Sample       friction Motor 1   Motor 2                                       ______________________________________                                        Example 1    0.093    11.4      8.2                                           A            0.110     2.8      4.2                                           ______________________________________                                    

In Examples 3 and 5 small round rods are produced with a diameter of 10mm. and a length of 15 mm. in which the tolerance precision of theexternal diameter is significant and in Example 4 calotte bearings areproduced with an internal diameter of 4 mm. Where it is a question ofthe tolerance precision of the internal diameter, greater demands areplaced on the dimensional stability of the internal diameter of thecalotte bearing than on the external diameter of round bars and even adimensional change during curing of 2 parts per 1,000 is consideredunacceptable and a dimensional change of 1 part per 1,000 at most isconsidered desirable.

To illustrate the influence of the ratio of the molding pressure to theweight of perfluoroalkylene polymers, the following processes werecarried out. The results are tablulated in Table I.

EXAMPLE 3

A mixture of 40 parts by weight of molybdenum sulfide and 40 parts byweight of zinc sulfide (component 1) was processed with 16.7 parts byweight of epoxy resin with an average epoxy equivalent of 525 and 3.3parts by weight cyclopentane tetracarboxylic acid dianhydride (compound2) according to the process described above, however, with the exclusionof polytetrafluoroethylene as the third component. The molding pressurewas 20 kp./mm.². After curing, the dimensional change of the externaldiameter was -5.3 parts per 1,000. The procedure was repeated using 10weight percent of PTFE and a pressure of 20 kp./mm.² and the dimensionalchange was 0.5 parts per 1,000.

When the same comparative experiment was carried out at 35 kp./mm.², andthe addition of PTFE was 5.5 parts, the results were 1.8 and 0 (seeTable I).

When the molding mixture contained 2 weight percent PTFE, a moldingpressure of 40 kp./mm.² was required in order to achieve dimensionalstability of 0 while a pressure of only 27 kp./mm.² was needed to causedimensional stability when the PTFE was present at 8 weight percent.

                  TABLE 1                                                         ______________________________________                                                       Pressure                                                                              Dimensional                                                           kp./mm..sup.2                                                                         change/1,000                                           ______________________________________                                        Weight percent PTFE:                                                          0                20        5.3                                                10               20        0.5                                                0                35        1.8                                                5.5              35        0                                                  2                40        0                                                  8                27        0                                                  ______________________________________                                    

It is surprising that according to the invention by addingpolytetrafluoroethylene as the third component of the molding mixtureand by using a molding pressure balanced to its a dimensional stabilityof the molding object can be strongly decreased during curing. Forcomparison purposes polytetrafluoroethylene alone was molded intoobjects in the same way as described for the above molding mixtures andsubjected to the same temperature cycle. When using a molding pressureof 20 kp./mm.² a dimensional change of -9.8 parts per 1,000 occurred andat a molding pressure of 35 kp./mm.² a dimensional change of -9.2 partsper 1,000.

The connection between the polytetrafluoroethylene content of themolding mixture and the molding pressure used on the one hand anddimensional change of the diameter during curing on the other hand is tobe seen even more clearly in Tables II and III which give the results ofprevious investigations.

Table II shows a dimensional change of the diameter during curing as afunction of the polytetrahydroethylene content of the molding mixture ata constant molding pressure of 20 kp./mm.² and 35 kp./mm.².

Table II shows a dimensional change of the diameter during curing as afunction of the applied molding pressure for molding mixtures with apolytetrafluoroethylene content of 2 weight percent and 8 weight percentas well as for polytetrafluoroethylene wax alone.

                  TABLE II                                                        ______________________________________                                                    Percent dimensional                                                           change                                                            ______________________________________                                                    20 kp./mm..sup.2                                                                        35 kp.mm..sup.2                                         ______________________________________                                        Percent PTFE:                                                                 2             -3.8        -0.6                                                4             -2.5        -0.2                                                6             -1.7        0.1                                                 8             -1.4        0.4                                                  10           -0.5        1.1                                                  12           -0.3        1.1                                                 ______________________________________                                    

                  TABLE III                                                       ______________________________________                                                      Percent dimensional change                                      ______________________________________                                                      PTFE   PTFE                                                                   (mixture)                                                                            (mixture)                                                              2 weight                                                                             8 weight PTFE                                                          percent                                                                              percent  alone                                           ______________________________________                                        Kp./mm.sup.2 pressure:                                                        15              -7.0     -3.0                                                 20              -3.8     -1.3     -9.7                                        25              -2.5     -0.4     -0.6                                        30              -1.4     0.5      -9.4                                        35              -0.5     0.5      -9.2                                        40               0       1.0                                                  45               0.1     1.4                                                  50               0.9     1.8                                                  ______________________________________                                    

It is essential that the above indicated series of the process stepsaccording to the invention be maintained as is shown in the followinginvestigation.

A final material was made in which the starting materials were as inExample 3, except only zinc sulfide was used alone. After the third stepof the process, molybdenum sulfide was added (the same amount as inExample 3) and the process was continued.

To one batch of this material, 15 weight percent of PTFE was added, (A)to the second batch no PTFE was added, (B) the compounds were thenmolded as in Example 3.

In (B), the dimensional change was 5.2 parts/1,000 but there was noshrinkage, there was swelling instead. In (A), the dimensional changewas +1.4 parts per 1,000.

EXAMPLE 4

The method of working of Example 1 was repeated with the exception thatcalotte bearings were produced. At a molding pressure of 35 kp./mm.²without the addition of polytetrafluoroethylene, a dimensional change ofthe internal diameter of -2.9 parts per 1,000 was determined. When amolding mixture containing 15% polytetrafluoromethylene wax was used atthe same molding pressure the dimensional change of the internaldiameter curing dropped back to -0.5 parts per 1,000.

EXAMPLE 5

From various mixtures of inorganic solids and solid epoxy resins with orwithout curing agent or cross-linking catalysts round bars were producedas in Example 1. The following mixtures were used:

                  (a)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2             22.3                                                    ZnS                   22.3                                                    CaF.sub.2             16.3                                                    Graphite              16.3                                                    Solid epoxide resin, EEW.sup.1 ca. 525                                                              19.0                                                    CPDA.sup.2             3.8                                                    ______________________________________                                         .sup.1 Epoxy equivalent weight.                                               .sup.2 Cyclopentanetetracarboxylic acid dianhydride.                     

                  (b)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2             28.3                                                    ZnO                   18.9                                                    CaF.sub.2             17.3                                                    Graphite              17.3                                                    Solid epoxide resin, EEW ca. 525                                                                    18.2                                                    ______________________________________                                    

                  (c)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2              6.3                                                    Kryolith              71.9                                                    Solid epoxide resin, EEW ca. 525                                                                    18.2                                                    CPDA                   3.6                                                    ______________________________________                                    

                  (d)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2             23.1                                                    ZnS                   23.1                                                    CaF.sub.2             16.9                                                    Graphite              16.9                                                    Solid epoxide resin, EEW ca. 525                                                                    20.0                                                    ______________________________________                                    

                  (e)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2             22.3                                                    ZnS                   22.3                                                    CaF.sub.2             16.3                                                    Graphite              16.3                                                    Solid epoxide resin, EEW ca. 245                                                                    19.0                                                    Methylene dianilin    3.8                                                     ______________________________________                                    

                  (f)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2             22.3                                                    ZnS                   22.3                                                    CaF.sub.2             16.3                                                    Graphite              16.3                                                    Solid epoxide resin, EEW ca. 600                                                                    20.3                                                    CPDA                   2.5                                                    ______________________________________                                    

                  (g)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2             22.3                                                    ZnS                   22.3                                                    CaF.sub.2             16.3                                                    Graphite              16.3                                                    Solid epoxide resin, EEW ca. 525                                                                    20.8                                                    Methylene dianilin     2.0                                                    ______________________________________                                    

                  (h)                                                             ______________________________________                                                              Parts by weight                                         MoS.sub.2             23.1                                                    ZnS                   23.1                                                    CaF.sub.2             16.9                                                    Graphite              16.9                                                    Solid epoxide resin, EEQ ca. 245                                                                    20.0                                                    ______________________________________                                    

In all cases a molding pressure of 35 kp./mm.² was used. By way of athird component thermally degraded polytetrafluoroethylene of thecommercial type in powder form was used. The following table shows thedimensional change of the external diameter of the molded object duringcuring in parts per 1,000 as a function of the content of PTFE in themolding mixtures.

    ______________________________________                                                Addition of PTFE (in percent)                                                 0     5       10      15    30                                        Mixture:                                                                      (a)       -3.9    -2.3    -1.8  -0.8                                          (b)       -1.9    -1.3    +0.2                                                (c)       -6.1    -5.4    -4.7  -3.9  -1.7                                    (d)       -2.9    -2.3    -1.8  -0.8                                          (e)       -2.6    -1.1    +0.3                                                (f)       -2.8    -1.9    -1.3                                                (g)       +2.5    +0.5                                                        (h)       -4.4    -3.5    -1.4                                                ______________________________________                                    

That which is claimed is:
 1. Cold molded self-lubricating bearing consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalents weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na₃ AlF₆ and FeF₂, and (c) 2-30 percent by weight of solid polytetrafluoroethylene having a molecular weight of 35,000 to 150,000 grams/mole and an average particle size of less than 0.075 mm. the percentages of (a), (b) and (c) being based on the total weight of the three components.
 2. The bearing as in claim 1, consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a solid thermosetting condensate of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)propane cross-linked with 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na₃ AlF₆ and FeF₂, and (c) .[.2-3.]. .Iadd.2-30 .Iaddend.percent by weight of a solid polytetrafluoroethylene having a molecular weight of 35,000 to 150,000 grams/mole and a particle size of less than 0.075 mm.
 3. Cold molded self-lubricating bearing consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na₃ AlF₆ and FeF₂, and (c) 2-30 percent by weight of a solid tetrafluoroethylene-perfluoropropylene copolymer with an average particle size of less than 0.075 mm. and a molecular weight of 35,000 to 150,000 grams/mole, the percentages of (a), (b) and (c) being based on the total weight of the three components.
 4. The bearing as in claim 3 consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a solid thermosetting condensate of epichlorohydrin and 2,2-bis(4-hydrophenyl)-propane cross-linked with 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH).sub. 2, CaF₂, Na₃ AlF₆ and FeF₂, and (c) 2-30 percent by weight of a solid tetrafluoroethylene-perfluoropropylene copolymer with an average particle size of less than 0.075 mm. and a molecular weight of 35,000 to 150,000 grams/mole, the percentages of (a), (b) and (c) being based on the total weight of the three components.
 5. The bearing as in claim 1 consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles of equal weights of MoS₂ and ZnS and, (c) 2-30 percent by weight of solid polytetrafluoroethylene with a molecular weight of 35,000 to 150,000 grams/mole and a particle size of less than 0.075.
 6. The bearing as in claim 3 consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles of equal weights of MoS₂ and ZnS, and (c) 2-30 percent by weight of a solid tetrafluoroethylene-perfluoropropylene copolymer with an average particle size of less than 0.075 mm. and a molecular weight of 35,000 to 150,000 grams/mole, the percentages of (a), (b) and (c) being based on the total weight of the three components.
 7. A composition for producing a cold molded self-lubricating bearing consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na.sub. 3 AlF₆ and FeF₂, and (c) 2-30 percent by weight of solid polytetrafluoroethylene having a molecular weight of 35,000 to 150,000 grams/mole and an average particle size of less than 0.075 mm. the percentages of (a), (b) and (c) being based on the total weight of the three components.
 8. The composition as claimed in claim 7 consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a solid thermosetting condensate of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)propane cross-linked with 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na₃ AlF₆ and FeF₂, and (c) 2-30 percent by weight of solid polytetrafluoroethylene with a molecular weight of 35,000 to 150,000 grams/mole and a particle size of less than 0.075 mm.
 9. A composition for producing a cold molded self-lubricating bearing consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH).sub. 2, CaF₂, Na₃ AlF₆ and FeF₂, and (c) 2-30 percent by weight of a solid tetrafluoroethylene-perfluoropropylene copolymer with an average particle size of less than 0.075 mm. and a molecular weight of 35,000 to 150,000 grams/mole, the percentages of (a), (b) and (c) being based on the total weight of the three components.
 10. The composition as claimed in claim 9 consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a solid thermosetting condensate of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane cross-linked with 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO Ca(OH)₂, CaF₂, Na₃ AlF.sub. 6 and FeF₂, and (c) 2-30 percent by weight of a solid tetrafluoroethylene-perfluoropropylene copolymer with an average particle size of less than 0.075 mm. and a molecular weight of 35,000 to 150,000 grams/mole, the percentages of (a), (b) and (c) being based on the total weight of the three components.
 11. The composition as claimed in claim 7 consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles of equal weights of MoS₂ and ZnS and, (c) 2-30 percent by weight of solid polytetrafluoroethylene with a molecular weight of 35,000 to 150,000 grams/mole and a particle size of less than 0.075 mm.
 12. The composition as claimed in claim 9 consisting essentially of(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane or condensates of epichlorohydrin and cycloaliphatic epoxy resins with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na₃ AlF₆ and FeF₂, and (c) 2-30 percent by weight of a solid tetrafluoroethylene-perfluoropropylene copolymer with an average particle size of less than 0.075 mm. and a molecular weight of 35,000 to 150,000 grams/mole, the percentages of (a), (b) and (c) being based on the total weight of the three components.
 13. A process for manufacturing cold molded self-lubricating bearings wherein the components(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na₃ AlF₆ and FeF₂, are(1) mixed and made into a powder; (2) plasticized and homogenized at a temperature above the softening temperature of Component (a); (3) repowdered and sieved to obtain a fraction with a particle size distribution consisting of at least 80 percent particles with a particle size of less than 0.315 mm. which are then intimately mixed with 2-30 weight percent of solid polyperfluoroalkylene selected from a group consisting of polytetrafluoroethylene or tetrafluoroethylene-perfluoropropylene copolymer or mixtures thereof having a molecular weight of 35,000 to 150,000 grams/mole and a particle size of less than 0.075 mm., and (4) molded in a steel multi-cavity die with a predetermined molding pressure of 15-50 kp./mm.³ at room temperature based on the amount of polyperfluoroalkylene added to the mixture, and (5) heating in an oven at increasing temperatures for specific time periods of 2 hours at 170° C., 2 hours at 200° C. and 4 hours at 230° C. to obtain the final molded product.
 14. A process for manufacturing cold molded self-lubricating bearings wherein the components(a) 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a curing, solid thermosetting epoxy resin consisting of condensates of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)-propane with epoxy equivalent weights of 200 to 1,000, (b) 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight of solid particles with an average particle size of less than 0.075 mm. which are inorganic solids selected from a group consisting of graphite, boron nitride, barium sulphate, glass fibers, asbestos, MoS₂, WS₂, ZnS, ZnO, PbO, Ca(OH)₂, CaF₂, Na₃ AlF₆ and FeF₂, are(1) mixed and made into a powder; (2) plasticized and homogenized at a temperature above the softening temperature of component (a); (3) repowdered and sieved to obtain a fraction with a particle size distribution consisting of at least 80 weight percent particles with a particle size of less than 0.315 mm. which are then intimately mixed with 2-30 weight percent of polytetrafluoroethylene-polyperfluoropropylene copolymer having a molecular weight of 35,000 to 150,000 grams/mole and a particle size of less than 0.075 mm., and (4) molded in a steel multi-cavity die with a predetermined molding pressure of 15-50 kp./mm.² at room temperature based on the amount of polyperfluoroalkylene added to the mixture, and (5) heating in an oven at increasing temperature for specific time periods of 2 hours at 170° C., 2 hours at 200° C. and 4 hours at 230° C. to obtain the final molded product.
 15. A process as in claim 13 wherein component (c) is 2-30 percent by weight of solid polytetrafluoroethylene having a molecular weight of 35,000 to 150,000 gram/mole and particle size of less than 0.075 mm.
 16. A process as in claim 13 wherein component (b) is present in 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight and consists essentially of a 50/50 equal weight mixture of MoS₂ and ZnS.
 17. A process as in claim 14 wherein the component (a) is 10-25 .[.percent.]. .Iadd.parts .Iaddend.by weight of a solid thermosetting condensate of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)propane cross-linked with 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride.
 18. A process as in claim 14 wherein component (b) is present in 90-75 .[.percent.]. .Iadd.parts .Iaddend.by weight and consists essentially of a 50/50 equal weight mixture of MoS₂ and ZnS.
 19. A process as claimed in claim 13 wherein component (c) is a mixture of polytetrafluoroethylene and polytetrafluoroethylene-perfluoropropylene copolymer. 